The present invention relates generally to electrical devices, and particularly to electrical power quality test circuitry for testing response of such devices to alternating power disturbances. This invention may be employed to test response of a variety of electrical devices such as controllers and equipment in industrial facilities, semiconductor tools, HVAC and so forth. In addition, this invention may be employed to provide high voltage testing of electrical devices such as control transformers, power supplies, control relays, etc.
Various electrical devices, such as those employed in industrial applications, are susceptible to malfunction or damage due to input power disturbances. For example, input power disturbances such as voltage sags and frequency disturbances may affect performance of the electrical devices and may reduce process productivity of applications where such devices are employed. Typically, electrical devices are tested with respect to utility power line disturbances such as variations in input voltage magnitude and duration. Further, several international standards have stipulated test procedures to qualify and accredit the electrical devices with respect to pre-defined test conditions.
Certain systems employ transformer-based test fixtures to emulate three-phase voltage dips, short interruptions and voltage variations for the electrical devices. For example, switching devices are employed in such fixtures to change the voltage through taps of the transformer. However, these test fixtures can only emulate voltage sags/swells, but cannot emulate frequency disturbances or grid harmonics. In addition, these systems are limited to discrete steps in voltage sags
Certain other systems employ amplifier-based test fixtures that include electronic power amplifiers connected to a signal generator. These signal generators are based on electronic circuits that may be able to generate various power disturbances but their power capability is generally limited and cannot provide the equipment under test with enough inrush current. As a result, such test may lead to misleading results.
Unfortunately, the transformer-based fixtures are unable to emulate certain power disturbances such as frequency changes, angle jumps, distorted grid voltage that include higher order time harmonics which are common in electrical devices. Furthermore, electronic amplifier based circuits have limited current capability.
Accordingly, it would be desirable to develop an integrated testing tool for testing response of electrical devices for a variety of power disturbances while meeting requirements of testing standards for such devices that require testing devices to provide the equipment under test with high inrush current.